1. Field of the Invention
The present invention relates to catalyst supports having coating containing metal oxide powder and also relates to a method to produce the same.
2. Related Background Art
Various catalysts have been developed such as catalysts for hydrogen production reaction to generate hydrogen as a fuel in fuel reforming systems such as fuel cells, and catalysts for the purification of exhaust gas to purify toxic components emitted from internal combustion engines like automobiles. Various kinds of substrates including honeycomb filters, on which a metal oxide such as alumina, and a noble metal such as platinum, rhodium and palladium are supported, have been generally used as such catalysts.
In general, powder obtained by wet grinding method has been heretofore used as such metal oxides. For example, Japanese Patent Application Laid-Open Gazettes No. Hei. 10-182155 (Document 1) and No. 2002-79097 (Document 2) disclose methods to obtain compound metal oxide powder by preparing oxide precursors from salt solutions of aluminum, cerium, and zirconium by coprecipitation method and then calcining the yielded oxide precursors in the air. In addition, in Japanese Patent Application Laid-Open Gazette No. Hei. 7-300315 (Document 3), a method is disclosed to obtain compound metal oxide powder by first adding boehmite alumina powder to a mixed solution of salt solutions of cerium and zirconium, and the mixture was then stirred followed by the drying and calcination of the resultant.
However, when conventional metal oxide powder like that described in Documents 1 to 3 is used, adhesion to substrates (especially to metal substrates) is not always sufficient and there is also a limitation for formation of thin film coating formed on the substrate. Therefore, it has been a problem because of difficulties in supporting such conventional metal oxide powder when using substrates such as metallic honeycomb filters and high density (high integration) honeycombs (e.g. microchannels equal to or greater than 1200 cell/inch2) with narrower tubular passages than those of common honeycomb filters, as well as limitation in the improvements of reforming performances.